The 93 and 95 Cobra R models are still $30K+. I think you were referring to the 2000 model that everyone was fast to speculate on. Even those are still $40K +.
The Thunderbird SC was a nice car, but unfortunately it never really caught on as being desirable with the young people. It was aimed more as a middle age persons luxuty performance vehicle. That is a stigma that is very hard to shake. Plus they werent easily modified.
I think most low production performance type domestic car/truck would hold their value well.
Cars on the list IMHO:
82-93 Fox Body 5.0 Mustangs and SVO's (People will someday get big money for these just like the 64 1/2-73 models. Cobra's will always bring more money. Even a nice 93 Model will still go for $10K+)
94-up Mustangs (The specialty models will be much more valuble as the years go by. Cobra's, Mystic colored cars, Bullits, etc. The problem with the SN95's is that they did not gain the notoriety that the Fox did. They were heavier and the 96-up models were not as inexpensively or easily modified as their 5.0 predecessors. Time will tell on these)
82-92 F bodies (especially 5.7 powered models or convertible models or 1LE package equipt cars or unusual models like the TTA)
93-2002 F bodies ( I would say that the specialty variations would bring money as collectibles. Cars such as the SLP Firehawks, Ram Air Trans Ams SS Camaros)
Corvettes as usual (you just cant knock them. most go down in value for a few years and then go back up again. You better believe that the ZR1 and the Z06 will bring big $$)
Ford Lightning pickups (any of the years)
91 GMC Syclone or 92-93 Typhoon
90-93 454 SS Chevrolet Pick ups (yes, they were slow, but they still are hot commodities)
Any 78-88 G body performance model or odd ball (Hurst Olds, 442's TR's, Monte SS, Grand Prix 2+2, Malibu's, EL Caminos, stick shift cars ,etc)
Any Viper
94-96 Impala SS (The 9C1 or other LT1 powered Caprices will probably be up there as well but not as desirable as the SS)
Mercury Marauders (Ford is supposed to discontinue this after the next model year. It has all the makings of a collector car being a performance type car with low production figures. I think popularity will dictate value in the coming years on this)
In conclusion, I think there will still be plenty to pick from.
What I have always wondered though is what will happen with all these high dollar GTO's, Chevelles, Impala's, early Mustangs, 55-57 type cars as the baby boomers start dying off. I dont think the Generation X'ers are anywhere near as successful or will have as much money to throw at collector cars as the baby boomers did. You will probably see prices come down as the markets become flooded with older cars that the young kids of today dont know of or have any interest in. This is all my opinion.